Internal combustion engines are well known and widely used as power sources. Applications for such engines range from small, hand-held machines such as chain saws to relatively large and complex propulsion and electrical power generation systems. Internal combustion engines may be used as primary power and propulsion sources, but may also have a wide variety of auxiliary systems coupled therewith.
On-highway trucks and other mobile work machines, for example, typically include several systems such as heating and cooling, hydraulic systems, air compressors, fuel and oil pumps, engine cooling systems, etc. operably coupled with a power output shaft of an internal combustion engine. During typical operation, the primary engine serves to not only propel such a work machine, but also to drive the various secondary systems. Decades of technological development have resulted in quite sophisticated and efficient engine systems, with a primary engine having a variable load range for powering different subsets of the various components. There are some instances, however, where powering of a secondary system of a work machine is desirable, but the full output power of a primary internal combustion engine is not needed. In addition, while the operating range of many internal combustion engines allows operation at relatively low loads, such operation may not always be optimally efficient or practicable.
It is well known that many on-highway trucks will often idle for extended periods of time, continuing to power various secondary systems of the work machine even when propulsion or other primary power is unnecessary. In particular, when a truck is parked the operator will often run the engine at an approximate idle speed, providing sufficient power to operate the heating or air conditioning system. While it is certainly convenient for an operator to simply park the truck at a truck stop, and keep the engine running, long periods of idling can consume appreciable amounts of fuel and result in wear and tear on the engine, even where the engine load is relatively small. In general terms, long periods of idling are an inefficient way in which to run a relatively large internal combustion engine, as heavy duty engines typically operate with approximately 20% thermal efficiency at idle conditions.
Some manufacturers have developed stand alone engines, known in the art as “pony” engines, which operate separately from a main engine and allow the main engine to be shut down when a truck or other mobile work machine is not traveling. These relatively smaller pony engines tend to have relatively higher efficiencies than the main engine due to lower friction and the ability to operate at a more practical load condition. Moreover, it is known to use the pony engine to assist in initiating operation of the main engine when desired.
In addition to such stand alone pony engines, a variety of other engine modifications have been introduced into the market that are also directed towards reducing energy waste. U.S. Pat. No. 4,996,845 to Kim provides a cooling/heating and power generating device that purportedly utilizes waste heat from an automobile to produce an auxiliary energy source for driving various accessories, including a cooling/heating apparatus, an electric generator, etc. Waste heat from the engine in the form of waste gases is passed through an exhaust tube to transfer heat to a heat exchanger and thenceforth to a cooling medium. Heat from the cooling medium may then be used to drive an expansion turbine to provide a source of power separate from the main engine. While Kim appears to provide one means of recovering energy in an internal combustion engine that might otherwise be lost, it requires that the main engine actually be operated, and therefore suffers from shortcomings similar to many known designs.
The present disclosure is directed to one or more of the problems or shortcomings set forth above.